Two years ago, billions of insect-like yet humanoid aliens called the Hephaestans invaded Earth. As humanity tried desperately to fight back, it was discovered that the Hephaestans were not unlike many bugs native to our planet in the sense that they required warm, wet conditions to survive. For this reason, civilians founded new "safe haven" cities in deserts and tundras, on mountains, and really any place that the Hephaestans could not survive in. While the official armies of the world decided on how to handle the situation from headquarters deep in safe territory, resistance groups formed on the borders between safe cities and seasonally dangerous areas. The Scavengers, for example, stationed themselves in the American Midwest, staying in Canada during fall and winter and moving down past the U.S.-Canadian border in spring to hold off the yearly arrival of alien expeditionary forces that seek to destroy the southernmost safe cities over the warm summer months. The Scavengers designed their own equipment made by their engineers, who formed ScavTech Industries, but anybody looking to join can still use custom equipment or surplus military weapons.